API extensions

• API for links cache, dramatically simplifying forms data binding:
  • All links created with Link.state are cached, and are recreated only when value is different.
  • const links = Link.all( this, 'attr1', 'attr2', ... ) makes sure that links for specified state members
    are cached, and returns the reference to the cache. Thus, links.attr1 is the direct reference to the link.
  • Links cache is directly accessible in render() with this.links.
• Link methods for purely functional updates of the enclosed object:
  • Links to arrays: unshift(...), push(...), splice(...) proxy call to native Array methods.
  • Links to arrays and objects: remove( key ) removes element with specified key.
  • Links to array and object members: remove() removes element from parent object or array.
• Methods for links to objects and arrays:
  • link.pick( key1, key2, ... ) creates an object with links to listed object members, in the same way as Link.all.
  • link.clone() creates shallow copy of the enclosed object.
• Added "Users List" application example.